1. Field of the Invention
This invention relates generally to electronic circuits for generating pseudo-random bit patterns. More particularly, the invention concerns a circuit that combines a cyclic redundancy check code generator and a pseudo-random number generator in such a way that the two generators share most of their common electronic elements.
2. Statement of Related Art
Both cyclic redundancy check code (CRCC) generator circuits and pseudo-random number generator circuits are well known individually. CRCC generator circuits have found widespread use in digital recording, satellite communications, and cable television data transmission systems to name but a few applications. See for example Creed et al. U.S. Pat. No. 4,549,298; Sechet et al. U.S. Pat. No. 4,354,201; Guillou U.S. Pat. No. 4,352,011; and Guillou U.S. Pat. No. 4,337,483. Pseudo-random number generator circuits have also found widespread use in integrated circuit testing, restricted access, cable and videotext subscription services, and a host of other applications. See for example Sechet et al. U.S. Pat. No. 4,354,201; Guillou U.S. Pat. No. 4,352,011; Davidson U.S. Pat. No. 4,320,509; Bass U.S. Pat. No. 4,291,386; Bass U.S. Pat. No. 4,222,514; and Lam et al. U.S. Pat. No. 4,216,374.
In some instances, particularly in the areas of integrated circuit testing and restricted access cable and videotext subscription services, CRCC generator and pseudo-random number generator circuits have both been used simultaneously, although not in the same circuit.
No one to my knowledge, however, has suggested combining the functions of a CRCC generator and a pseudo-random number generator in a single circuit wherein common electronic circuit elements are shared rather than duplicated as in prior art applications. Such a circuit design in discrete logic form provides cost advantages due to the decrease in the number of electronic circuit elements required. Moreover, improvements in energy consumption are obtained for the same reason. In integrated circuit form the advantages of the proposed design also include the conservation of precious substrate space which can then be used for the fabrication of additional logic elements.
Accordingly, it is an object of the invention to provide a simplified circuit design that combines the functions of a CRCC generator and a pseudo-random number generator, and wherein the two generators share common electronic components.
It is another object of the invention to provide such a circuit having means for easily and quickly controlling the mode of operation.
It is yet another object of the invention to provide such a circuit particularly adapted to generate CRC codes for ensuring accurate data transmission and reception and selected pseudo-random bit sequences for use as restricted access codes.